Motor control.



1. EATON.

moron comm. APPLICATION FILED NOV-9| f9l6- RENEWED JAN. 25. IQIB- 1,297, 121. Patentgd Mim- 11, 1919 v 51?. BR. 613R.

Inventor" John Eaton,

a Mew;

His Jfttorneg.

UNITED STATES PATENT OFFICE.

JOHN EATON, OF SCHENEGTADY, N E VZ 'E IORK, ASSIGNOLR. TO GENERAL ELECTRIC COMPANY, A CORIORATION OF NEW YORK.

MOTOR CONTROL.

1,297,121. Patented Mar. 11, 1919. Application filed November 3,1916, Serial No. 130,470. Renewed January 25, 1919. Serial No. 273,170.

Specification of Letters Patent.

To all whom it may concern: tor, the work would be advanced against the Be it known that I, JOHN EATON, subject cutters, the cutter teeth would be broken ofi', 1

residin at S tate and possibly the entire machine wrecked.

of the King of Great Britain,

. The same result would happen if the feed Schenectady, county of Schenectady,

of New York, have invented'certain new and motor should continue running after the.

useful Improvementsin Motor Controls, of cutting motor when it is desired to stop the which the following is aspecification. machine, or if abnormal circuit conditions My invention relates to the control of should occur, such as afailure of voltage or electric motors and it provides improved an overload on the motors causing the line means whereby the motors may be star ed circuit breaker to open.

and 'stopped and generally controlled in a One of the objects of my invention is to safe, reliable, and eflective manner. provide a control for a milling machine or More specifically, my invention relates to the lilgw whereby thedriving motors will be the control of a plurality of mechanically cotirdinated so as to cooperate practically independent electric motors which cooperate perfectly; that is, be started or stopped to produce a certam result and which must practically simultaneously at the will of the be coordlnately started and stopped; that IS, operator and be generally controlled so as to be started practically simultaneously and be brought to rest practically simultaneously.

although each motor drives a separate load. A particular instance of the necessity for such a control occurs in the electric drive for milling machines and the like, the motors of which are connected to drive separate cooperating parts of the machine, although in a certain limited degree the loads on the motors are interdependent. Such machines are ordinarily provided with a motor, called the feed motor, for advancing and withdrawing the work to and from the cutters as desired. Another motor called the cutting, motor, is provided for rotating the cutters as the work is advanced toward the cutters by the feed motor. The cutting motor has usually the greater load and is ordinarily a much larger motor than'the feed motor, and in order to get the best results from the operation of these motors, they are ordinarily required to have different speedtorque and other characteristics. They must also be provided with means for varyingthe relative speeds of the motors so as to vary the relative speeds of the feed mechanism and the cooperating cutters to accommodate the machine to various classes of work. These motors, although of different capacities and having mechanically independent.

rotating elements which drive cooperating parts of the machine at different speeds, must nevertheless 'be controlled in such a manner that they will cooperate perfectly at all times. They must be coordinated so as to start or stop practically simultaneously, sinre for instance, if the feed motor should start before or quicke than the cutting moavoid the dangers which I have above pointed out. In carrylng my invention into efl'ect I provide a control for the feed and cutting braking circuit, thus bringing the motors to rest simultaneously, the arrangement 'further providing that the motors will be auto: matically dynamically braked and brought .to rest simultaneously more quickly in an emergency o upon the occurrence of abnormal circuit conditions. Furthermore, I provide a plurality of push buttons and automatic' devices for controlling the motors so that there is practically no chance for the motors or the driven machine to be injured either by negligence on the'part of the operator or by the occurrence of conditions which are beyond the operators control. By merely pressing the proper one of the plurality of push buttons, the operator can control the operation of the machine as dediagrammatically one embodiment of my invention, A represents the armature, F the shunt field and F the commutating field of an electric motor for driving the cutters of rest simultaneously in an emergency, and

' a milling machine or the like, and a represents the armature, f the shuntfield and f the commutating of an' electric motor for driving the feed mechanismof the same I speed-torque and other characteristics than the feed'mbtor. The direction of rotation I 5 of these motors is controlled by four electrotively, for driving in the forward or cutting magnetic switches or contactors, two .for

each direction of rotation. Two of theseswitches. are designated as C and C, respec direction, while the. other'two switches, designated as R and B, respectively, when closed drive the machine in the opposlte or return direction. These four switches are operated by shunt windings controlled by the push buttons- 1, 2, 3, and 4. The push button 1 is provided for starting the motors simultaneously in the cutting direction,.the push button 2 for starting the motors simultaneously in thereverse direction, the push button 3for bringing thevmotors quickly to the push'button' 4 is provided :foristopping 'the motors simultaneously when the operator desires to stop the machine temporarily for any reason.

In the drawing the parts are shown in the position they assume when thecircuit breaker C.-- B. is open and all parts'deener-v gized. The manual switch 5 is provided for operating the cutting motor alone or both the cuttingmotorand the feed motor to gether-as desired. By moving this switch to the right the armature circuits and the shunt field circuits of the two machines-are connected in parallel so that the movements of the two motors 'm'ay be coordinated. With the switch 5- closed, when the line is energized by the closing of the circuit breaker 'C. B. and the push button 1 is pressed, the contactors C and C are energized in parallel across the line andthe two motors will be energized to start in the out ting direction simultaneously. Similarly, with the line energized, the motors may be simultaneously started in the opposite or return direction by pressing the pushbut ton 2 thereby energlzing the windings'of contactors R and R across the line. The starting resistances S. R. and S R are provided forboth motors andzthese resistances are controlled by means of the contactors 5 and 7. These contactors are of the well known series 'type which have windings carrying the motor current and are held mined value, when they close and are held closed by'magnetic force. The contactor 6 in closing short circuits the resistance S. R

and the contactor 7 in closing short circuits both sections of resistance and the coil of contactor 6, causing the 'contactor to open.

Contactor 7 is maintained closed by meansof a maintaining coil '8 energized across the line through an interlock 9 when the contactor and interlock 25 on eontactor (1 close. When the motors are energized to pperate in the return direction the limitlng resistance L. R. is included in the armature circuit of the motors in addition to the starting resistances S. R. and S. R so that the motors will have a low speed when operating in this direction since when it is desired to re verse the operation ofthe machine it is usually required that the -move quite slowly. I c For varying. the speed of' each motor sinparts of the machine dependently of the speed of the other-motor Ihave provided two rheostats, one of .which "is connected in the shunt field circuit; of the cutting motor'and has a resistance 1' controlled by the arms, while the other rheostat has a resistance 1" connected in the shunt field of the feed motor and controlled bythe arm 8'. When the motor is started-these rheostats are short circuited by means. of they relayflO, the coil of which is energized across the line through the interlock 9 associated with the series contactor 7. These shunt fieldrheos'tats will be short 'circuited' until the series contactor 7 closes and'moves theinterlock 9 against its bias to open the coil circuit of relay'lO' and include the portions of the resistances 1" and r in the shunt fields of the cutting motor and the feed motor, re X spectively, as determined by the setting of the arms 8 and. s. The operation of this in-- terlock-Qis substantially the same as that described in my application" Serial No.

817,365, filed Feb. 6,- 1914, motor control systems, and assigned to the same assignee as this applicatio i In. order to bring -.-the m'otor armatures to rest, simultaneously I provide a brake resistance through whichthe motor armatures are short circuited. This brake resistanceis. divided into two sections B. R. and B. R. The purpose of these two sections of resistance is to graduate the dynamic braking current as'the shunt field of the cutting mo tor builds up and the motors slow down. llor making the dynamic braking connectlons I. provide the contactor B. This con tactor is normally held closed by means of a spring 11. The winding of this contactor' is' open until the current drops to a predeter tactors C, C, R, R, and B are arranged as illustration I shave shown them pivoted at their middle points and engaged by upwardly projecting stems of two adjacent .contactors in the closed position. The opprevious United States Patent No. 1,041,845 issued to E. J. Murphy and myself, and will be sufficiently clear without further description. While the contactor B is closed by a spring thisspring is not sufiiciently stifl' to applyany considerable pressure to the contacts hence electromagnetic means are provided for holding the contacts tightly closed.

The brake resistance B. R.-is controlled by means of the electromagnetic switch or contactor 16 which is provided with a winding having one terminal connected to the shunt field of.,the cutting motor and the other end connected to the resistance r in this shunt field circuit. The winding of this relay is dividedinto two halves which are differentially wound or opposed to each other, so that when the two halves are energized they neutralize each other and the relaywill notclose. Itis obvious that when the relay 10 isopen, the shunt field current of the cutting motor must pass through the two diflerential sections of the winding of this contactor and through any of the resistance 1 which. may be inserted in the field circuit to the negative side of the line. The contactor' is therefore inoperative under this condition. When, however, the relay 10 is closed, the lower half of the winding of contactor 16 and'the resistancer are short circuited so that one half the winding is energized and the 'contactor becomes active. The winding of this contactor isso fadjust'ed that when the .field current approaches a maximum, that is, when the field F is nearly full strength the contactor will close, but when the field is weak the con tactor willnot close even though only one of the windings is energized. When the 'relay 1O closes, the field resistance r is short circuited so as to strengthen the shunt field F of the cutting motor, but the field increases gradually due to the inductive efiect.

and until the field current rises to the predetermined value, which is preferably near the maximum, the contactor 16 will not op-' erate. When it' does operate it short circuits a section of brake resistance B; R. The operation of this .contactor is substantially the same as that of the relay 23 of the Patent #1,041,8&5 above mentioned, and it is thought that further description is unnecessary. This specific feature of my invention is broadly claimed in the United States patent to Brobst, No. 1,943,799.

In order to immediately stop the motors simultaneously in an emergency or upon the occurrence of abnormal circuit conditions such as the failure of voltage or an overload on the motors, I provide a circuit breaker O. B. which is so arranged as to apply an effective dynamic brake to the motors to bring the motors to rest simultaneously very quickly when the circuit breaker opens. To this end, in the particular form illustrated, I have provided two contacts 17 and 18 which move into and out of engagement with fixed contacts as the circuit breaker opens and closes. The contact 18 engages with three contacts, two of which close. a dynamic braking circuit through themotor armatures and the emergency brake resistance E. B. R, While the other contact is connected with the shunt fields so as to include the shunt fields of the motors in parallel with the emergency brake resistance E. B. R. across the motor armatures. When the circuit breaker is open the circuit of the motor armatures is immediately closed through the resistance E. B. R. and the shunt fields of the motors. are connected across themotor armatures in parallel with E. B. R., the arrangement being such that the rheostats in'the shunt field circuits are excluded and the motors given full field excitation. The emergency brake resistance E. B. R. is less than the combined resistances of B. R. and B. B so that the motors maybe brought to rest simultaneously in the shortest possible time consistent with safety for the motors The circuit breaker push button 3 and the emergency braking circuit will be made as above explained. The operation of this circuit breaker is substantially the same as that disclosed and claimed in my application Ser. No. 817 ,365, filed Feb. 7, 1914, and assigned to the. same assignee as this application.

1 As thus constructed and arranged the operation of my device is as follows:

If it isdesired that the feed motor and the cutting motor coiiperate to'drive the milling machine, the manual switch'5 is first closed, thus connecting the armatures and shunt field circuits of both motors in multiple. Preparatory to starting,- the circuit breaker C. B. is closed, energizing the no-voltage re' Is-wound contactor. 16 and this contactor a "motors ,.are thus energized to full strength,- the circuit for the fields being from the posi- 10, the other path branching through shunt field'f of the feedmotor, right'hand contact Q10 member of switch and uppercontact of -relay '10,"both paths joining and passing z through conductor24c to the negative supply conductor... The relay in closing short circuits the lower coil of the difi'erenti 1 close when the field -F has builtup to nearly the maximum-strength. The closing of this contactorproduces. no effect on the motor at this time since the braking resistance is 20 not included in the motor circuits. In order to start the motors simultaneously in the cuttin direction, the push button 1 is now presse thus'eflergizing the coils of the con tactors'. O and G,'-caus1ng.these contactors 25 to close and complete the circuit for-the mo- .tor 'armatures, the circuit for the coils of.

. these 'contactorsbeing from the positive'supply conductor through stop push button 4,

I push button 1,- conductor 22, to the negative so supply conductor. -The contactor C in clos- .lng, closes aninterlock'25 which com letes a maintaining circuit for the coils 0 con- ,"tactors-C- and Cthrough the conductor 26 exclusive of the push button 1, permitting 3'5 this'buttonto bereleased and the contactors nevertheless remain energized. The mechanical interlock 12 associated with the contactor-O will open the normally closed I contacts of dynamic brake contactor Band. 40 this contactor. will benmaintained open as long as I the contactor- 0- remains closed. When the'contactors' G and C close; the coil of contactor B is energized in shunt to the" armatures of the motors but it willnot close when the counter E. M. F. of the mol 0I'S builds lip-because of the restraining ef-- iect of interlock 12. The dynamic braking circuit 1s thus maintained open, until'it is desired that it shallbe closed," as, for. in-

stance, when ,it-is desired to stop-the inachine orwhen the voltage fails-or in case i themot-orsjarei overloadedg The two motors T -";will simultaneously beginas rotate with full-- 'fieldl'andjjstart'the feedmechan'sm and cut-"sf /ters simultaneously inthe cu ting, direction, .jthearm'atu're circuit for the motors ng from the positive supplyfco nductor,

1, starting resistance -R., coil of series contactor 6,]start1n resistance S. R,.contact nco member s'bf linen ntactor 0', through the-- armature'circuits of the two motors in mule tiple, contact-"members .ofcontactor. C, to.- th 'e'nega tive supply conductpn The motors will-istart at a rate of speed depending upon thejalnountof-startin'g {resistance W en - tactorfi will close, thus short circuiting the starting resistance S. R andsimultaneously including the series coil of series contactor 7 in the motor armature circuit. When the armature current again drops to a rede-. termined value, the series contactor will close, placing a short circuit around the starting resistances S. R. and S. R., thus con- 7, necting the motor armatures directly across the source of supply. As the series contactor 7 closes, its contact member en ges the interlock 9 and moves the intefidck against it bias into engagement with. its left hand contact, thereby opening the circuit of relay .10, causing thetrelay to drop its contacts and remove the short circuits from the shunt field resistances r and 1", at the same time 8 oftthe series contactor- 7 through a circuit from the source of'positi've supply conductor, push button 4, conductor 26, interlock 25, interlock 9,.conductor 21, conductor 22 to the negative supply conductor. The motors willthen increase in speed depending upon the amount of the variable resis shoes 'I, 1" in their shunt field circuits. The opening of the relay 10, removingthe short circuit from the shunt fields resistances, included both of the coils of the contactor 16 in the circuit of the shunt field F of the cutting motor, and this contactor will be opened since the two coils of the contactor' oppose 100 eachothen The speeds of the motors may be independently varied by means of the arms 8 and 8' provided for varying the shunt' field resistances. If at any time current in the armature circuits should exceed theipredetermined. values for which the serie re;

[lays 27 and 27 included in the arm ture circuits of the feed and cutting motors, respectively, have been set, these relays will close their contacts and .temporarily' short circuit the resistances r and 1, respectively, in the shunt fields of .the motolgs, thus decreasing the speed ofthe motors and limit-. ing value of their armature currents. If it is. desired to temporarily stop the machine, thepush button 4 is ressed, there by opening-the coil circuits '0 the line con 'tactors' C and C and the maintaining coil offseries contactor 7, causing these contactors to open ftheir switch members, disoon necting the motor armatures" from the source of supply and-removing! short circuit from the starting resistancesS. R. and S Rflpreparatoryto againjstarting themotors. As I soon as the contactor'C opens, the mechanical interlock-12 noj'longer' hold the 1 dynamic brake contactoi 13:10 m, :and this contactorsgllose in .accprdaflgy fghit biasto the cljo p fiwhe y m t- 1 cally connecting thca motoif 'l -armature 13o:

cuits in multiple with the dynamic brake resistances B R and B R. The coil of contactor B will be still connected in shunt to the motor armatures and will maintain the contactor closed as long as the armatures rotate. The opening of series contactor 7 causes the interlock 9 to be moved into engagement with its right hand contact member in'accordance with its bias thus energizing the coil of relay 10 through a circuit previously described. The relay 10 will close its contact members, thereby completing a short circuit about the shunt field resistances 7' and r, and giving full field strength for the motors fora large dynamic braking effort. The lower contact member of relay 10 in closing not only short circuits the shunt field resistance 1" "in the field F of thecutting motor but also short circuits the lower coil of the differentially wound contactor 16. This contactor however will not close until substantially the full field urrent flows \through the shunt field F, as previously explained, thus automatically providing a certain time interval before the resistance in the dynamic braking circuit is reduced. When the shunt field F has been built up to substantially its full strength,

- the motors will-have decreased'in speed considerably so that ,when the contactor 16 closes its contacts and short circuits the dynamic brake resistance B R, the retardation of the motors will be accomplished in a smooth and gradual manner." The motors are now operating as generators and send a dynamic braking current through the resistances B. R. and B R, and'since their 'armatures and fields are electrically con nected, the movements of the two armatures will be coordinated and the two motors will stop simultaneously.

By pressing the push button 1, the motors may be again'started in the cutting direc-i members of reverse contactor B, through the motor armatures in multiple, limiting resistance L. R, contact members'of reverse co'ntactor R to the other negative supply conductor. The motors will accelerate as before but a reverse direction, but they .Wlll not come up to. the normal speed because ofthe limiting resistaiice LR. which is provided for giving a decreased speed for all the operations in the reverse direction. Reverse contactor R in closing likewise opens the contacts of dynamic brake cont actor 'B through its mechanical interlock entirely disconnected from the source of supply "and'that the motors be brought to rest simultaneously in a very short interval of time, the push button 3 isdepressed thereby opening the circuit breaker C. B., disconnecting the motors 'and the control apparatus from thesource of supply.

soon as the circuit breaker C. B. opens, its interlock 18 includes the motor armatures in an emergency dynamic braking circuit, the circuit for the armatures being from the interlock 18 through the emergency brake resistance E. B..R.,.through both motor 'armatures in multiple back again to the interlock 18. Depressing the safety stop push button 3 not only causes the line switch to open but also deenergizes the coil of relay 19, causing this relay to drop its contacts and connect the fields of the motors in shunt to their armatures, the circuit being-from one side of the armature circuit at the interlock ,18 of C. B. through conductor 28 to a shunt circuit, one path of which is through 'the conductor 29, shunt field F, the other shunt path being through the conductor 30,- contacts of relay l9, righthand switch member of manual switch 5, shunt field f, joining the other shunt path and passing through the conductor 23, conductor 20, conductor 31 through the interlock 17 of C. B; to the other end of the emergency dynamic brake resistance E. B. R., thereby connecting the shunt .fields in multiple to their 'armatures across the resistance E. B. B.

through circuits exclusive of the shunt field rheostats. The motors will thereby be included in an emergency dynamic braking circuit and will have the greatest dynamic braking effort consistent with the capacity of the motors. I The motors will be brought to rest simultaneously as before but more;

quickly.

With the motors running in either the-forward or reverse dir'ection,if at any time the sourceof-supply should fail, the 110-voltage release magnet 32 of the circuit breaker of C. B. will 'bedeenergized and the circuit breaker will be caused to open.

opening of the. circuit breaker from any gency dynamicbraking circuit heretofore explained in connection with the operation I An overload on the motors will likewise cause the circuit breaker'to open by means of'the over- 'loadcoil 33 releasing the catch 34.; The

, cause will automatically complete the emerdescribed after pressing the safety stop push button 3,

If it is desired to operate the cutting mo-- tor alone and feed the Work to the cutters manually the switch 5 is opened thus disconnecting the armature and field of the feed motor F. M. from the source of, supply. The

cutting motor may then be operated in the same manner as that explained in connection plied with current from themotor armatures with the operation of the two motors together.

What I claim as new and desire to secure byLetters Patent of the United States, is

1. The combination with a plurality of cooperating electric motors connected to separate loads, of means for automatically bringing the motors to rest simultaneously comprising a dynamic braln'ng circuit supplied with current from both motor armatures.

2. The combination with a plurality of,cooperating electric motors of d fferent capacities connected to a source of supply and driv-.

ing separate loads of different values at different. speeds, of means for automatically bringing the motors to rest simultaneously, comprising a dynamic braking circuit supoperating in multiple.

, ues, of means for automatically bringing the 3. The combination with a plurality of motors having mechanically independent rotatingelements connected to coiiperating parts of a machine, of means for automatically bringing the "motors to rest simultaneously comprising a-dynamic brake resistance connected to-the motor armaturesoperating in multiple;

4. The combination. with a plurality of motors of difl'erent capacities drivin cooperating parts of a machine, the sai motors having separate loads of different val;

motors to rest simultaneously comprising a dynamic braking circuit supplied with cur rent from the motor armatures operating in multiple. Y

operatin stopping the motors simultaneously comprising a dynamic brakingcircuit supplied with 7 current from the motor armatures.

v 6.," The combination with a plurality of 00 operating shunt wound-motors connected to separate loads, of means for connecting the motors to 'a source of supply 'to start the loads simultaneously, and means for discon-J 5.- .The combination with a plurality of co electric motors having mechani cally in epen'dent rotating elements. driving separate loads, of means for varying the rel v ative speeds of themotors', an-d 'means for necting the armatures and shu nt fields of the motors from the source of supply and automatically connectin armatures in parallel-wlth a resistance to dynamically brake the motors and bring them'to rest simultaneously.

7. The combination with a plurality of difi'erent ca acity motors having shunt fields, the sald motors connected in parallel to a source of supply and driving separate loads of different values consisting of cooperating parts of a machine, of a resistance for dynamically braking the motors, and

said. fields and v means for'disconnecting the motor arma- *tures from the source of supply and automatically connecting said armatures in parallel with the resistance to dynamically brake the motors and bring-the coiiperating'parts ofthe machine to rest simultaneously.

operating electric motors having shunt fields, each of the motors driving a separate load, of means comprising a plurality of push buttons for starting, stopping and reversing the motors, means including one of said push buttons for connecting the motors to a source of supply, means including. another of said push buttons for disconnecting thelmotor armatures from the source of supply and automatically including a dynamic braking resistance in the circuit of the motor armatures operating in parallel to bring the motors to rest simultaneously, meanslncluding another of said push buttons for disconnecting the fields and armatures of said motors from the source of supply: and automatically connecting said fields and armatures .in parallel with another resistance of less value to dynamically brake the motors and bring them simultaneously to rest more quickly.

', In witness whereof, I have hereunto set myhand this Sth day'pf November, 1916."

OHN EATON. 

